Field of the Invention
The invention generally relates to systems and methods for integrating thermochemical processing of biomass (e.g., lignocellulosic materials) and anaerobic digestion. In particular, the invention provides systems and methods in which the byproducts of thermochemical biomass processing (e.g., torrefaction, pyrolysis, gasification) procedures such as light oxygenated organic compounds, are converted to methane by anaerobic digestion.
Background of the Invention
Thermochemical processing of lignocellulosic plant material (e.g., torrefaction, pyrolysis, and gasification) is of great interest with respect to developing alternative energy sources. These processes employ heat and catalysts to transform plant material into useful fuels which can replace traditional fuels such as oil and coal. The plant matter that is processed may be purposefully obtained for thermochemical processing, or may be “waste” material or a byproduct from other processes. Waste and byproducts are especially attractive for use, since this eliminates the need for their disposal, and instead converts them to useful substances.
During the pyrolysis of lignocellulosic materials, a sizable fraction of the biomass (8-15 mass %) is converted into light oxygenated organic compounds. These small organic compounds can be condensed and recovered in the form of an aqueous fraction containing between 10-50 mass % of organics. Formic acid, acetic acid, propionic acid, methanol (wood alcohol), glycoaldehyde, and acetol are the main light oxygenated organic compounds produced by thermochemical processing. These small organic compounds can also be produced during the torrefaction and gasification of lignocellulosic materials.
During the 19th and the 20th centuries most of the methanol, acetic acid and acetone consumed in the world was produced by refining aqueous fractions produced by the slow pyrolysis of wood (wood distillation). With the creation and expansion of the petroleum industry in the first half of the 20th century and with the development of cheaper catalytic routes to produce methanol, the interest in producing and utilizing light oxygenated organic compounds via biomass thermochemical processing disappeared. In fact, the production of these small molecules is currently considered a serious environmental problem, limiting the deployment of pyrolysis and torrefaction units for bio-fuel and bio-power production. There is a need in the art for efficient and cost effective means for processing the light organic materials produced from thermochemical processing. This could be a boon to the alternative energy field by solving the problem of disposal of the byproducts of thermochemical bio-fuel generation.